DMM Working Group A. Yegin
Internet-Draft Actility
Intended status: Informational D. Moses
Expires: July 28, 2018 Intel
K. Kweon
J. Lee
J. Park
Samsung
S. Jeon
Sungkyunkwan University
January 24, 2018
On Demand Mobility Managementdraft-ietf-dmm-ondemand-mobility-13
Abstract
Applications differ with respect to whether they need IP session
continuity and/or IP address reachability. The network providing the
same type of service to any mobile host and any application running
on the host yields inefficiencies. This document describes a
solution for taking the application needs into account by selectively
providing IP session continuity and IP address reachability on a per-
socket basis.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 28, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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session continuity. IP session continuity is essential for mobile
hosts to maintain ongoing flows without any interruption.
IP address reachability: The ability to maintain the same IP address
for an extended period of time. The IP address stays the same across
independent IP sessions, and even in the absence of any IP session.
The IP address may be published in a long-term registry (e.g., DNS),
and is made available for serving incoming (e.g., TCP) connections.
IP address reachability is essential for mobile hosts to use
specific/published IP addresses.
Mobile IP is designed to provide both IP session continuity and IP
address reachability to mobile hosts. Architectures utilizing these
protocols (e.g., 3GPP, 3GPP2, WIMAX) ensure that any mobile host
attached to the compliant networks can enjoy these benefits. Any
application running on these mobile hosts is subjected to the same
treatment with respect to IP session continuity and IP address
reachability.
It should be noted that in reality not every application may need
these benefits. IP address reachability is required for applications
running as servers (e.g., a web server running on the mobile host).
But, a typical client application (e.g., web browser) does not
necessarily require IP address reachability. Similarly, IP session
continuity is not required for all types of applications either.
Applications performing brief communication (e.g., ping) can survive
without having IP session continuity support.
Achieving IP session continuity and IP address reachability with
Mobile IP incurs some cost. Mobile IP protocol forces the mobile
host's IP traffic to traverse a centrally-located router (Home Agent,
HA), which incurs additional transmission latency and use of
additional network resources, adds to the network CAPEX and OPEX, and
decreases the reliability of the network due to the introduction of a
single point of failure [RFC7333]. Therefore, IP session continuity
and IP address reachability should be provided only when necessary.
Furthermore, when an application needs session continuity, it may be
able to satisfy that need by using a solution above the IP layer,
such as MPTCP [RFC6824], SIP mobility [RFC3261], or an application-
layer mobility solution. These higher-layer solutions are not
subject to the same issues that arise with the use of Mobile IP since
they can utilize the most direct data path between the end-points.
But, if Mobile IP is being applied to the mobile host, the higher-
layer protocols are rendered useless because their operation is
inhibited by Mobile IP. Since Mobile IP ensures that the IP address
of the mobile host remains fixed (despite the location and movement
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of the mobile host), the higher-layer protocols never detect the IP-
layer change and never engage in mobility management.
This document proposes a solution for applications running on mobile
hosts to indicate whether they need IP session continuity or IP
address reachability. The network protocol stack on the mobile host,
in conjunction with the network infrastructure, would provide the
required type of IP service. It is for the benefit of both the users
and the network operators not to engage an extra level of service
unless it is absolutely necessary. It is expected that applications
and networks compliant with this specification would utilize this
solution to use network resources more efficiently.
2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Solution3.1. Types of IP Addresses
Four types of IP addresses are defined with respect to mobility
management.
- Fixed IP Address
A Fixed IP address is an address with a guarantee to be valid for a
very long time, regardless of whether it is being used in any packet
to/from the mobile host, or whether or not the mobile host is
connected to the network, or whether it moves from one point-of-
attachment to another (with a different IP prefix) while it is
connected.
Fixed IP addresses are required by applications that need both IP
session continuity and IP address reachability.
- Session-lasting IP Address
A session-lasting IP address is an address with a guarantee to be
valid throughout the IP session(s) for which it was requested. It is
guaranteed to be valid even after the mobile host had moved from one
point-of-attachment to another (with a different IP prefix).
Session-lasting IP addresses are required by applications that need
IP session continuity but do not need IP address reachability.
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- Non-persistent IP Address
This type of IP address does not provide IP session continuity nor IP
address reachability. The IP address is created from an IP prefix
that is obtained from the serving IP gateway and is not maintained
across gateway changes. In other words, the IP prefix may be
released and replaced by a new one when the IP gateway changes due to
the movement of the mobile host forcing the creation of a new source
IP address with the updated allocated IP prefix.
- Graceful Replacement IP Address
In some cases, the network cannot guarantee the validity of the
provided IP prefix throughout the duration of the IP session, but can
provide a limited graceful period of time in which both the original
IP prefix and a new one are valid. This enables the application some
flexibility in the transition from the existing source IP address to
the new one.
This gracefulness is still better than the non-persistence type of
address for applications that can handle a change in their source IP
address but require that extra flexibility.
Applications running as servers at a published IP address require a
Fixed IP Address. Long-standing applications (e.g., an SSH session)
may also require this type of address. Enterprise applications that
connect to an enterprise network via virtual LAN require a Fixed IP
Address.
Applications with short-lived transient IP sessions can use Session-
lasting IP Addresses. For example: Web browsers.
Applications with very short IP sessions, such as DNS clients and
instant messengers, can utilize Non-persistent IP Addresses. Even
though they could very well use Fixed or Session-lasting IP
Addresses, the transmission latency would be minimized when a Non-
persistent IP Addresses are used.
Applications that can tolerate a short interruption in connectivity
can use the Graceful-replacement IP addresses. For example, a
streaming client that has buffering capabilities.
3.2. Granularity of Selection
IP address type selection is made on a per-socket granularity.
Different parts of the same application may have different needs.
For example, the control-plane of an application may require a Fixed
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IP Address in order to stay reachable, whereas the data-plane of the
same application may be satisfied with a Session-lasting IP Address.
3.3. On Demand Nature
At any point in time, a mobile host may have a combination of IP
addresses configured. Zero or more Non-persistent, zero or more
Session-lasting, zero or more Fixed and zero or more Graceful-
Replacement IP addresses may be configured by the IP stack of the
host. The combination may be as a result of the host policy,
application demand, or a mix of the two.
When an application requires a specific type of IP address and such
an address is not already configured on the host, the IP stack shall
attempt to configure one. For example, a host may not always have a
Session-lasting IP address available. When an application requests
one, the IP stack shall make an attempt to configure one by issuing a
request to the network (see Section 3.4 below for more details). If
the operation fails, the IP stack shall fail the associated socket
request and return an error. If successful, a Session-lasting IP
Address gets configured on the mobile host. If another socket
requests a Session-lasting IP address at a later time, the same IP
address may be served to that socket as well. When the last socket
using the same configured IP address is closed, the IP address may be
released or kept for future applications that may be launched and
require a Session-lasting IP address.
In some cases it might be preferable for the mobile host to request a
new Session-lasting IP address for a new opening of an IP session
(even though one was already assigned to the mobile host by the
network and might be in use in a different, already active IP
session). It is outside the scope of this specification to define
criteria for choosing to use available addresses or choosing to
request new ones. It supports both alternatives (and any
combination).
It is outside the scope of this specification to define how the host
requests a specific type of prefix and how the network indicates the
type of prefix in its advertisement or in its reply to a request).
The following are matters of policy, which may be dictated by the
host itself, the network operator, or the system architecture
standard:
- The initial set of IP addresses configured on the host at boot
time.
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- Permission to grant various types of IP addresses to a requesting
application.
- Determination of a default address type when an application does
not make any explicit indication, whether it already supports the
required API or it is just a legacy application.
3.4. Conveying the Desired Address Type
[RFC5014] introduced the ability of applications to influence the
source address selection with the IPV6_ADDR_PREFERENCE option at the
IPPROTO_IPV6 level. This option is used with setsockopt() and
getsockopt() calls to set/get address selection preferences.
Extending this further by adding more flags does not work when a
request for an address of a certain type results in requiring the IP
stack to wait for the network to provide the desired source IP prefix
and hence causing the setsockopt() call to block until the prefix is
allocated (or an error indication from the network is received).
Alternatively a new Socket API is defined - getsc() which allows
applications to express their desired type of session continuity
service. The new getsc() API will return an IPv6 address that is
associated with the desired session continuity service and with
status information indicating whether or not the desired service was
provided.
An application that wishes to secure a desired service will call
getsc() with the service type definition and a place to contain the
provided IP address, and call bind() to associate that IP address
with the Socket (See pseudo-code example in Section 4 below).
When the IP stack is required to use a source IP address of a
specified type, it can use an existing address, or request a new IP
prefix (of the same type) from the network and create a new one. If
the host does not already have an IPv6 prefix of that specific type,
it must request one from the network.
Using an existing address from an existing prefix is faster but might
yield a less optimal route (if a hand-off event occurred after its
configuration). On the other hand, acquiring a new IP prefix from
the network may be slower due to signaling exchange with the network.
Applications can control the stack's operation by setting a new flag
- ON_NET flag - which directs the IP stack whether to use a
preconfigured source IP address (if exists) or to request a new IPv6
prefix from the current serving network and configure a new IP
address.
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Internet-Draft On Demand Mobility January 20185. Backwards Compatibility Considerations
Backwards compatibility support is required by the following 3 types
of entities:
- The Applications on the mobile host
- The IP stack in the mobile host
- The network infrastructure
5.1. Applications
Legacy applications that do not support the OnDemand functionality
will use the legacy API and will not be able to take advantage of the
On-Demand Mobility feature.
Applications using the new OnDemand functionality must be aware that
they may be executed in legacy environments that do not support it.
Such environments may include a legacy IP stack on the mobile host,
legacy network infrastructure, or both. In either case, the API will
return an error code and the invoking applications may just give up
and use legacy calls.
5.2. IP Stack in the Mobile Host
New IP stacks must continue to support all legacy operations. If an
application does not use On-Demand functionality, the IP stack must
respond in a legacy manner.
If the network infrastructure supports On-Demand functionality, the
IP stack should follow the application request: If the application
requests a specific address type, the stack should forward this
request to the network. If the application does not request an
address type, the IP stack must not request an address type and leave
it to the network's default behavior to choose the type of the
allocated IP prefix. If an IP prefix was already allocated to the
host, the IP stack uses it and may not request a new one from the
network.
5.3. Network Infrastructure
The network infrastructure may or may not support the On-Demand
functionality. How the IP stack on the host and the network
infrastructure behave in case of a compatibility issue is outside the
scope of this API specification.
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Internet-Draft On Demand Mobility January 20185.4. Merging this work with RFC5014
[RFC5014] defines new flags that may be used with setsockopt() to
influence source IP address selection for a socket. The list of
flags include: source home address, care-of address, temporary
address, public address CGA (Cryptographically Created Address) and
non-CGA. When applications require session continuity service and
use setsc() and bind(), they should not set the flags specified in
[RFC5014].
However, if an application sets a specific option using setsockopt()
with one of the flags specified in [RFC5014] and also selects a
source IP address using setsc() and bind() the IP address that was
generated by setsc() and bound using bind() will be the one used by
traffic generated using that socket and options set by setsockopt()
will be ignored.
If bind() was not invoked after setsc() by the application, the IP
address generated by setsc() will not be used and traffic generated
by the socket will use a source IP address that complies with the
options selected by setsockopt().
6. Summary of New Definitions6.1. New APIs
setsc() enables applications to request a specific type of source IP
address in terms of session continuity. Its definition is:
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int setsc (int sockfd, in6_addr *sourceAddress, sc_type addressType) ;
Where:
- sockfd - is the socket descriptor of the socket with which a
specific address type is associated
- sourceAddress - is a pointer to an area allocated for setsc() to place
the generated source IP address of the desired session
continuity type
- addressType - Is the desired type of session continuity service.
It is a 3-bit field containing one of the following
values:
0 - Reserved
1 - FIXED_IPV6_ADDRESS
2 - SESSION_LASTING_IPV6_ADDRESS
3 - NON_PERSISTENT_IPV6_ADDRESS
4 - GRACEFUL_REPLACEMENT_IPV6_ADDRESS
5-7 - Reserved
setsc() returns the status of the operation:
- 0 - Address was successfully generated
- EAI_REQUIREDIPNOTSUPPORTED - the required service type is not supported
- EAI_REQUIREDIPFAILED - the network could not fulfill the desired request
setsc() may block the invoking thread if it triggers the TCP/IP stack
to request a new IP prefix from the network to construct the desired
source IP address. If an IP prefix with the desired session
continuity features already exists (was previously allocated to the
mobile host) and the stack is not required to request a new one as a
result of setting the IPV6_REQUIRE_SRC_ON_NET flag (defined below),
setsc() may return immediately with the constructed IP address and
will not block the thread.
6.2. New Flags
The following flag is added to the list of flags in the
IPV6_ADDR_PREFERENCE option at the IPPROTO6 level:
IPV6_REQUIRE_SRC_ON_NET - set IP stack address allocation behavior
If set, the IP stack will request a new IPv6 prefix of the desired
type from the current serving network and configure a new source IP
address. If reset, the IP stack will use a preconfigured one if it
exists. If there is no preconfigured IP address of the desired type,
a new prefix will be requested and used for creating the IP address.
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Internet-Draft On Demand Mobility January 20187. Security Considerations
The setting of certain IP address type on a given socket may be
restricted to privileged applications. For example, a Fixed IP
Address may be provided as a premium service and only certain
applications may be allowed to use them. Setting and enforcement of
such privileges are outside the scope of this document.
8. IANA Considerations
This document has no IANA considerations.
9. Contributors
This document was merged with [I-D.sijeon-dmm-use-cases-api-source].
We would like to acknowledge the contribution of the following people
to that document as well:
Sergio Figueiredo
Altran Research, France
Email: sergio.figueiredo@altran.com
Younghan Kim
Soongsil University, Korea
Email: younghak@ssu.ac.kr
John Kaippallimalil
Huawei, USA
Email: john.kaippallimalil@huawei.com
10. Acknowledgements
We would like to thank Wu-chi Feng, Alexandru Petrescu, Jouni
Korhonen, Sri Gundavelli, Dave Dolson and Lorenzo Colitti for their
valuable comments and suggestions on this work.
11. References11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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